Apparatus for steam generator control



Dec. 17, 1946. I J, D. MCCRACKEN 2,412,739

APPARATUS FOR STEAM GENERATOR CONTROL Filed May 7, 1943 Patented Dec. 17,1946

APPARATUS FOR STEAM GENERATOR CONTROL James D. McCracken, Chicago, Askania Regulator Company,

corporation of Illinois Application May 7, 1943', Serial No. 486,050

4 Claims. 1

The invention relates generally to apparatus for steam generator control, and more particularly to the control of combustible material flow to the steam generator.

Modern, high pressure, steam generators or boilers are designed to generate steam at very high rates and to have relatively small capacity for storing heat energy. As a result, such generators or boilers are highly responsive to the energy input, that is, the supply of fuel and combustion air and are, therefore, capable of following relatively rapid changes in load or steam demand. An ideal method of controlling such a steam generator would be to change the supply of fuel and of combustion air concurrently with load. Such an ideal control might be approximated by having the means for supplying fuel and the means for supplying combustion air both directly responsive to or controlled by the load. Such a method of control will hereinafter be referred to as the parallel method or system. This method of control, however, has one particular disadvantage, namely, the possibilityof feeding straight fuel to the boiler in the absence of combustion air should there be a failure of the combustion air supply equipment or its control. The results of such feeding of fuel without combustion air are sufiiciently disastrous in these modern steam generators that a second type or method of control has heretofore been employed.

This second method or type of control will hereinafter be referred to as the series method and consists in having the load call for the required combustion air and the air flow in turn call for the corresponding fuel. In this way, no fuel is supplied to the boiler without the required amount of combustion air being available. This method, therefore, eliminates the particularly serious disadvantage of the parallel method, but has its own disadvantages, some of which will presently be mentioned.

Though controls have been perfected until, in some instances, they operate substantially simultaneously with the change in load or demand, there is inherently in such control devices some element of time lag, and as one control device acts on another, and that one in turn on still another, this time lag accumulates and builds up until it is substantial. There is even a greater time lag in the devices that are governed by the controls as, for example, the combustion air supplying means in a boiler. Thus in the case of the "series method, there is, first, the time lag in the controls responsive to the change in load. There is next the time lag in the combustion air ferred apparatus.

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2 in supplying means. Next there is the time lag in the controls which are responsive to the supply of combustion air and which govern the means supplying the fuel. Inasmuch as these time lags are all additive, a very substantial time lag exists, resulting in numerous undesirable conditions, in-. cluding hunting and initial, considerable excess supply of combustion air with anincrease in load and, conversely, an initial excess fuel supply for a large decrease in load.

It is an object of this invention, therefore, to provide a new and improved apparatus for steam generator control. 7

Another object of the invention is to obtain increased stability of control and to obtain such increa'sedstability by a simple method and apparatus.

A further object is to provide a method of controlwhereby a condition to be satisfied by adjustment of two variables calls for or governs directly all of a first variable and simultaneously part only of a second variable, the remainder of the second variable being called for or governed by the first variable. 7

Another object is to provide a new apparatus for steam generator control which attains to a degree the simultaneity of response of the parallel system without, however, incurring the risk of disastrously excessive fuel supply over com bustion air supply, an inherent disadvantage of the parallel system.

Still another object is to provide a new appa. ratus for steam generator control which assures operation of the combustion air control and supply means before the fuel supply means can respond in full to an increase in load, but at the same time attains a moreprompt response of the fuel supply than can be obtained by the series system.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawing, composed of a single, diagrammatic figure.

The method of this invention has a great variety of applications andmay be practicedby different types of apparatus. It is, however, particularly well adapted for the control of a steam generator and will, for purposes of disclosure, be described hereinafter as adapted to such control of a steam generator and as practiced by a pre- It is not intended, however, .that the invention is to be limited to the particular disclosure. On the contrary, it is intended to cover all adaptations of the method and all modifications or alternative constructions of the apparatus falling within the scope and spirit of the invention as defined by the appended claims.

In its broad aspects, the invention provides a method of control whereby a condition to be satisfied by the adjustment of two variables calls for or governs directly all of a first variable and simultaneously part only of a second variable, the remainder of the second variable being called for or governed by the first variable. In a steam generator the condition to be satisfied is, of course, the steam demand or the load on the generator. The two variables are fuel and combustion air which must be supplied in such quantities as to fill the demand for steam and also, of course, in such ratio as to insure proper combustion of the fuel.

In a modern steam generator, the supply of combustion air for any considerable length of time without a supply, or at least an adequate supply, of fuel is, undesirable and harmful but not disastrous. However, the feeding of fuel in the absence of combustion air produces results which not only are undesirable and harmful but which may be classed as disastrous. Accordingly, in the method of this invention as applied to the control of a steam generator, the combustion air is the variable which is governed directly and completely by the condition to be satisfied and the fuel is made the variable which is partially governed directly by the condition to be satisfied and partially governed by or made responsive to the supply of combustion air, so as to assure that an excessive supply of fuel in the absence of combustion air does not occur.

In the drawing, there is shown diagrammatically a preferred apparatus for practicing the method of this invention. As shown, I represents a boiler or steam generator having a steam header 2, a combustion air intake or supply conduit 3, a fuel supply conduit 4, here shown as projecting into and discharging in the direction of the combustion air supply conduit, and an up-stack or exhaust conduit 5- for the products of combustion. Thecontroller for the combustion air supply is herein shown diagrammatically as a damper 6 located in the up-stack 5. It is to be understood that this is a purely symbolic showing intended to represent any type of controller for the combustion air supply. In actual practice, such controllers take a variety of forms, in-' cluding exhaust fans, blowers or other devices which may be driven by electric motors or by steam turbines, directly or through hydraulic couplings or various other media in an attempt to attain regulation without hunting. All of such controllers, whether complicated or simple, director indirect, have some time lag in their operation. The fuel supply, likewise, is diagrammatically shown as controlled by a damper I located in the fuel supply conduit 4. This again is intended purely as a symbolic showing, representative of any type of controller for the fuel supply, whether that be one adapted for the control ofgas, liquid fuel, powdered coal, or a stoker. These control means, likewise, have an inherent time lag.

It is known that the pressure in the header 2 is a measure of the load or the steam demand on the boiler or steam generator I and when properly utilized and interpreted may be employed to control the supply of fuel and combustion air to.

the steamgenerator. Herein the control apparatus utilizes this steam header pressure as an indication of the load or steam demand, that is, ofthe changing condition to be satisfied at all 4 times, and translates that demand into an appropriate and proportional supply of fuel and of combustion air. To that end, there is provided a first or master regulator 8 which translates the steam header pressure into a measure of steam demand, a second regulator 9 which will hereinafter be referred to as the load regulator or the combustion air controller regulator, and a third regulator II] which will hereinafter be known and referred to as a combustion or fuel regulator.

. The regulators are each Askania regulators embodying the well known Askania jet pipe principle.

More particularly, the master regulator 8 comprises a weight ll selected to maintain a desired pressure in the drum of the steam generator or boiler. Opposing the action of this weight is a pressure responsive device I2 connected by a conduit 13 to the steam header 2. The weight H and the pressure responsive device l2, through an appropriate lever system It, act on an Askania jet pipe l5 through which air under pressure is flowing. Disposed opposite the nozzle of the jet pipe I5 is an orifice l6 forming one terminus of a conduit H which is connected to a pressure responsive device [8' arranged to act on the jet pipe [5 in opposition to the weight II. It will be seen from the foregoing that the primary impulse for the masterregulator is the pressure in the steam header 2 as modified by the weight H, while the secondary impulse is the pressure created in the pressure responsive device IS, the regulator reaching a state of balance when the two impulses equally affect the jet pipe 15. The regulator 8' may thus be said to be an equilibrium device.

The second or load regulator 9 comprises an Askania jet pipe 20 through which a fluid under pressure, preferably oil, is flowing. Disposed opposite the nozzle of the jet pipe 20 are a pair of orifices 2|. The right hand one of these is by a conduit 22 connected to one port of a hydraulic motor 23, whilethe other of the, orifices is by a. conduit 24 connected to the other port of the hydraulic motor. The motor 23 is here shown as a piston and cylinder device and is operatively connected to govern the combustion air supply controller represented by the damper 5. The regulator 9 receives its primary impulse from the master regulator 8, and to that end is provided with a first pressure responsive device 25 which is by a conduit 28 connected to the conduit ll to be subjected to the pressure in that conduit, which is a measure of the steam demand or load on the boiler. The pressure responsive device 25 is, of course, so arranged as to tend to move the jet pipe 23 in such direction as to cause an increase of flow through the up-stack 5, that is, an increase in the quantity of combustion air sup.- plied. 'In order to maintain a metered relationship between the steam demand and the combustion air flow which in turn, under proper operation and after initial adjustments made, is proportional to the energy supplied to the boiler, the

' secondary impulse on the load regulator 9 is the combustion air flow. To that end the reguluator has a second pressure responsive device 21 acting in opposition to the first device 25; Herein the' combustion air flow is. measured by the pressure drop across the boiler and, accordingly, the pressure responsive device 27 has opposite sides thereof connected by conduits 2'8 and 29; respectively, to appropriate pointsof the boiler.

The combustion or fuel regulator lll comprises an Askania jet pipe 30 through which, as in'the case of the regulator 9, a fluid under pressure, preferably oil, is flowing. Disposed opposite the nozzle of the jet pipe are a pair of orifices 3|, the right hand one of which is by a conduit 32 connected to one port of a hydraulic motor 33, while the other orifice is, through a conduit 34, connected to the opposite port of the motor 33. Herein the motor 33 is shown as a piston and cylinder device operatively' associated to govern the fuel supply controller, herein symbolically illustrated as the damper 1.-

In order to obtain a more immediate response than is obtainable by the series method of regulation and yet eliminate the hazards and disastrous results of the parallel system of regulation, the'fuel supply in this invention is, as above stated, governed partially directly by the steam demand and partially by the flow of combustion air. To that end the regulator In is supplied with two primary impulses; one the steam demand, the other the combustion air flow. Accordingly, the regulator is provided with a first pressure responsive device 35 which is by a conduit 35 connected to the conduit 23 and hence is subjected to the air pressure generated in master regulator, which air pressure is proportional to the steam demand or load. The device 35 is, of course, arranged to urge the jet pipe 30 in such direction as to cause an increase in the supply of fuel. A second pressure responsive device 3! has its opposite sides connected by conduits 38 and 39 to the conduits 28 and 25, respectively, so as to be responsive to the combustion air flow through the boiler I. The second pressure responsive device 37 is connected to act in the same direction as the pressure responsive device 35 and the two are so adjusted that an appropriate variation in the fuel supply is obtained for each variation in the steam demand. It will also be understood that the percentage of control which each of the devices 35 and 3'! exercises may be varied so that the fuel supply may be made ten per cent directly responsive to the steam demand and ninety per cent responsive to the combustion air flow, or the fuel supply may be made twenty per cent, thirty per cent, and so forth, directly responsive to steam demand, and correspondingly less responsive to combustion air flow to fit any desired condition.

The secondary impulse of the combustion regulator ii! is, of course, the actual fuel supply, and to that end the regulator ID has a third pressure responsive device 43 intended to receive an impulse proportional to the actual fuel supply. The manner in which this actual fuel supply is measured may take a variety of forms depending upon the character of the fuel. Therefore, the measuring means illustrated in the drawing is again but symbolic of any suitable measuring means; Herein a restriction 4| in the fuel supply conduit 4 is shown with conduits t2 and 43 connected at one of their ends to the conduit l on opposite sides of the restriction and at their remaining ends to opposite sides of the pressure responsive device so to indicate, by the pressure differential on opposite sides of the restriction,

the quantity of fuel supplied. The regulators 9 and it, like the regulator 8, may appropriately be described as, equilibrium devices.

As an aid to a better understanding of the method andof the. function of the apparatus, the operation thereof for a typical example will be described briefly. Let it be assumed, therefore, that there has been an increase in the steam demand or load on the boiler. Under those condithe conduit I! of the crease in [the supply tions, the pressure in the header 2 will drop and this pressure change will, through the conduit I3, be [transmitted to the pressure responsive device l2. As a consequence, weight I I will overcome the pressure responsive device l2 and, through the lever system M, will pivot the jet pipe H3 in such direction that the jet of air discharged therefrom will strike more directly upon the orifice l6. This movement of the jet pipe I5 continues until the pressure in the conduit l'l, acting through the pressure responsive device I3, is suficient ,to equalize the force exerted by the lever system I 4 thereby bringing the jet pipe It? to rest in this new equalized position. The pressure in the conduits 26 and 36 is thus proportional to the steam demand and through the pressure responsive device acts as the primary impulse on the regulator 9 and causes the jet pipe 20 thereof to be pivoted in a direction to cause movement of the controller 6 in such direction as to increase the flow of combustion air. The movement of the jet pipe 20 under this primary impulse is arrested and eventually stabilized by the pressure responsive device 21 which receives [the secondary impulse to which the regulator is subjected, namely, a measure of the combustion air flow through the boiler.

Simultaneously with this increase in steam demand, or at least as nearly so as sensitive controls can make it, and without waiting for the increased combustion air flow to take place, which is delayed not only by the time lag in the controls but also in the means for producing the increased supply of combustion air, a partial inof fuel is obtained. This partially direct control of the fuel regulator Ill by the steam demand. This steam demand is directly reflected on the regulator ll) through the conduit 36 and the pressure responsive device 35, and functions to pivot the jet pipe in a direction to bring about an increased fuel supply. The regulator I ii in response to this impulse directly from the master regulator 8 is, of course, adjusted to bring about a portion only of the total increase in fueLnecessary to satisfy the increase in steam demand. While the percentage of the increased fuel supply thus obtained in direct response to the increase in steam demand may be varied to satisfy different conditions, this percentage in steam generators is preferably something less than fifty per cent. Large steam generators are, for economic reasons, usually not; operated onlow loads. Furthermore, at the loads at which large steam generators are operated a partial increase in fuel supply without a corresponding increase in the combustion air supply can take place without disastrous results. As a. consequence, a portion of the fuel supply may be under the direct control of the steam demand to gain the advantage of more prompt response without the possibilities of disastrous results should the controls not function to bring about an increased combustion air supply. The balance of the fuel supply is under the control of combustion air flow, and to that end receives its impulse from the difference in air pressure on the opposite sides of the boiler. The pressure responsive device 37 which receive this second primary impulse aids the device and between the two a full increase in the fuel supply commensurate with the increased steam demand is obtained. The actual fuel supply createsthe secondary impulse imparted to the regulator Hi and, through the pressure responsive device 40, arrests the movement of the jet pipe 30 when the results because of the full increase in fuel supply called for has been met.

It is believed apparent from the foregoing that I have provided a vastly improved method of and apparatus for the control of two variables, and particularly a method of and apparatus for controlling the supply of fuel and combustion air in a steam generator. My invention, among other things, decreases hunting and it does so not by a suppression of the oscillations, but by elimination of the cause for'such oscillations. It is the time lag between a change in demand and the fulfillment of the conditions satisfying that changed demand which causes hunting, and this time leg'is reduced by at least partially increasing or decreasing the energy input to the steam generator substantially concurrently with the change in demand. This, moreover, is accomplished without the possibility of disastrous results in the event of combustion air supply failure.

I claim as my invention:

1. Control apparatus for a steam generator or the like comprising, in combination, a master regulator responsive to the pressure of the steam of the steam generator and operable to generate a fluid pressure signal proportional to the steam pressure; a first device for controlling the combustion air supply to the steam generator; a first fluid actuated power means for adjusting said first device; a, second device for controlling the fuel supply to the steam generator; 2. second fluid actuated power means for adjusting said second device; combustion air flow measuring means; a second regulator for translating the signal of said master regulator into a fluid pressure signal applied to said first power means, said second regulator being connected to said first power means to permit of the supply of fluid pressure thereto and including a first pressure responsive means connected to said master regulator to receive the signal generated thereby and a second pressure responsive means acting in opposition to said first means and connected to said combustion air flow measuring means; and a third regulator operable to translate the signal of said master regulator and a signal generated entirely by combustion air flow through the steam generator into a fluid pressure signal governing a portion of the fuel supply in direct response to the master signal and the balance of the fuel supply in response to the combustion air flow only, said third regulator being connected to said second power means to supply fluid thereto and including a first pressure responsive means connected to said master regulator to receive the signal generated thereby, a second means connected directly and only to said combustion air flow measuring means, and a third means connected to be responsive to the rate of fuel supply adapted to balance said last named first and second means when the fuel supply equals the combined demand of the master regulator and the combustion air flow.

2. Control apparatus for a steam generator or the like having a header comprising, in combination, a master signal generator responsive to the pressure in the header and operable to generate a signal representative of the load on the steam generator; a first device for controlling the combustion air supply to the steam generator; power 7 means for adjusting said first device; a second device for controlling the fuel supply to the steam generator; a power means for adjusting said second device; means for measuring thecombustion air flow through the steam generator; 9. second signal generator connected to control the power means for said first device including afirst means connected and responsive to said master signal generator to receive the signal generated thereby and a second means acting in opposition to said first means and connected to said combustion air fiow measuring means; and a third signal generator connected to control the power means for said second device including a first means connected and responsive to said master signal generator to receive the signal generated thereby and partially to regulate the fuel supply directly in accordance with the load on the steam generator, and a second means connected directly and only to said combustion air flow measuring means partially to regulate the fuel supply in accordance with combustion air flow.

3. Control apparatus for a steam generator or the like having a header comprising, in combination, a master signal generator responsive to the pressure in the header and operable to generate a signal representative of the load on the steam generator; a first device for controlling the combustion air supply to the steam generator; power means for adjusting said first device; a second device for controlling the fuel supply to the steam generator; a power means for adjusting said second device; means for measuring the combustion air flow through the steam generator; a'seoond signal generator including an equilibrium device connected to control the power means for said first device and connected to be responsive to said master regulator to adjust the air supply entirely and proportionally in response to the load; and a third signal generator connected to control the power means for said second device and connected to said master regulator and to said combustion air flow measuring means to regulate the fuel supply partially directly in accordance with the load on the steam generator and partially directly in accordance with the combustion air flow only. a

4. In a control apparatus for a steam generater or the like, a master regulator connected to be responsive to a primary impulse indicative of the load on the steam generator and to a secondary impulse generated by the regulator in response and proportional to the primary impulse to which it is subjected; a combustion air supply controller; a second regulator connected to govern said combustion air supply controller and connected to be responsive to the secondary impulse of said master regulator acting as a pri mary impulse and to an impulse proportional to the flow of combustion air through the steam generator acting as a secondary impulse whereby the supply of air is varied in direct proportion to the load; a fuel supply controller; and a regulator connect-ed to govern said fuel supply controller, said last named regulator being connected tosaid master regulator to be responsive to the secondary impulse or? said master regulator to control a portion or the fuel supply directly and immediately in response to the load on the steam 7 generator and also connected tobe responsive directly to an impulse constituting the combustion air supply exclusively, to govern the balance of the fuel supply in accordance with the combustion air supply only.

JAMES D. MCCRACKEN.

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